A. Field
The present invention concerns a monofilament string.
B. Related Art
This mainly includes, but is not limited to, a monofilament string that can be used for stringing rackets for ball sports such as, for example, tennis, squash, racket ball, badminton and the like.
The invention however also concerns a monofilamentstring or thread that can be used for, for example, fishing, or in musical instruments, etcetera.
More specifically, the invention is intended for a polymer string or thread that is manufactured as monofilament in a bicomponent extrusion process and that consists of various polymers that are arranged in a clearly set pattern in accordance with the so-called ‘island in the sea’ concept compared to each other.
This concept consists of using various polymers or polymer mixtures separately in the same monofilament string, and arrange them in such a geometrical manner versus one another that, if one looks at a cross-section of the manufactured string, this appears to be a manifold of separate cores or ‘little islands’, shaped by a certain polymer or a group of polymers, surrounded and kept in place by a matrix or ‘sea’, mainly but not necessarily exclusively consisting of another polymer or a group of other polymers.
In order to provide optimum strength and tensile strength, a mixture of two or more various polymers can be chosen, or yet another polymer or group of polymers can be used that consists of linearly segmented block copolymers that contain a sequence of hard and soft segments.
The polymer or the polymer mixture of the ‘sea component’ is at first chosen in such a way that it displays an optimum compatibility, especially an optimum bonding to the ‘island components’.
Furthermore, the ‘sea component’ preferably contains a polymer elastomer, for example a thermoplastic polyether polyester elastomer, which decreases stiffness and improves the elasticity of the part of the string that surrounds the ‘island components’ without negatively influencing the recovery of the string after elastic distortion, so that a constant quality of the string can be guaranteed over a long period of use.
The invention also concerns a method for manufacturing such a string.
In practice one already knows various sorts of polymer strings that distinguish themselves from each other both as far as their construction and as far as their composition are concerned.
However, these types of strings all have their own typical characteristics, together with the specific advantages and disadvantages that come with them.
With this not only their physical, chemical and sensory characteristics are meant, such as for example elasticity modulus, breakage and tensile strength, tension relaxation, loop strength, abrasion resistance, resistance against influences of high humidity, temperature, radiation and/or the like.
But also their playing characteristics, in professional terms indicated with power and control, ball sensitivity and touch, comfort, spin, performance, elasticity, ball speed, etc.
It is also important how these characteristics materialise under different playing conditions, such as for example how the ball control behaves both when playing soft and when playing hard.
In general, it can be stated that the player should experience the same ball feeling both when playing soft and when playing hard.
Also, these characteristics should include the sound that is produced by the impact of the ball or the shuttle on the string.
This is indeed regarded as essential for the success of the game.
Sound is namely used as sign of recognition when exchanging hits.
Especially in the case of badminton the most sought-after strings produce a certain sound that can so far only be reproduced by the use of natural strings or by a specific sort of polymer strings.
In this context strings for tennis rackets made of natural gut are generally known.
They are made of animal gut that is processed by means of a time-consuming and complex procedure.
The primary characteristics hereof are superior elasticity, tension stability, and liveliness.
On the other hand, these strings are rather expensive and sensitive to weather conditions, especially to high humidity.
Furthermore strings for tennis rackets are known that are based on a polymer basis and that are designed either as monofilament or as multifilament, and this in strongly deviating shapes.
Mostly, the monofilament strings consist of a single thread of polyester or aromatic polyamides, provided with a thin outer protection and finishing layer.
It is generally assumed that the diameter of this, especially for tennis strings, is between 1.1 to 1.35 mm and for badminton strings for example between 0.6 to 0.8 mm, which is mainly decisive for the eventual playing characteristics that can range from elastic to durable.
The strings were mostly experienced as relatively stiff but on the other hand generally have a higher durability.
They often also have the tendency to relatively quickly loose their tension, as a result of which the control diminishes and the string feels ‘dead’.
It is generally assumed that the monofilamentstrings allow for a better control of the ball when playing hard, but that this could still be improved when playing soft.
They are also not capable, especially in the case of badminton, to produce the desired sound upon impact of the shuttle or ball.
This sound namely serves as a sign of recognition when exchanging hits and is generally regarded as essential for the success of the game.
Classical are on the other hand multifilament strings, in which often a large amount of microfibres, possibly designed from various materials, are twined into a same string that is subsequently provided with a resisting cover layer.
As advantage of these multifilament strings their high elasticity is mentioned mostly.
It is generally assumed that the multifilament strings allow for a better control of the ball when playing soft, but that this could still be improved when playing hard, as opposed to monofilament strings.
These type of strings furthermore have the disadvantage that they tend to snap as soon as the protective layer is damaged.
For this reason they are therefore mostly experienced as vulnerable.
Furthermore, because of their complex structure and complicated production method, they are fairly expensive, since the separate filaments first have to be woven to a string before they can subsequently be embedded in a matrix.
Poor bonding of this matrix to the interwoven multifilament strings and letting loose of the various constituting parts (defoliation, delamination) is a known disadvantage hereof and constitutes an important limitation of their useful lifespan.
Also generally known is the use of hybrid strings, which is understood to mean that a different type of strings is used for the stringing of a racket lengthwise, e.g. monofilament strings as discussed above, compared to the stringing widthwise, where for example multifilament strings find their application.
However, these hybrid strings lead to difficulties when optimally stringing a racket, and it is not uncommon to have to call upon more complicated stringing techniques.
In JP 2007330772 of the company Toray Monofilament Co., a monofilamentstring is described of the ‘island in the sea structure’ in which the ‘island components’ consist of a thermoplastic polyester in which 1 to 40 percent by weight of the polymer is replaced by the same material that is used for the creation of the surrounding ‘sea component’, the latter namely consisting of at least a thermoplastic polyamide, fluorinated polymer, or a polyolefin, but preferably of a polyamide.
The number of ‘island components’ is between 7 and 25.
The diameter of the string is typically 0.5 to 1.5 mm and the tensile strength 3.0 to 8.0 cN/dtex.
The shape and arrangement within the thread of the island components is not specifically determined, however.
Still it is stated that triangles, round shapes, rectangles, leaf shapes with three or five sided branches are possible, however, without indicating specific advantages of a specific shape or arrangement or expressing a preference.
Also, it is stated that a symmetric arrangement is possible, with which in the aforementioned context a rotational spiral-shaped symmetry is intended, as is usual for tennis strings and can be realised or imposed only by torque, twining or twisting from the outside, and which is therefore no inherent characteristic of a specific island structure of the string.
On the other hand, JP 2007282661 of the company Gosen KK, describes a monofilament string, also of the ‘island in the sea structure’, for 40-90 percent by weight consisting of an ‘island component’ and for 10-60 percent by weight of a ‘sea component’ and in which at least 13 island components are present.
The ‘island components’ are shaped in this from at least one polyamide, polyester or polyolefin, with a preference for a polyamide, and have a diameter of 0.05 to 0.2 mm.
In that, the ‘sea component’ consists of at least one thermoplastic elastomer polyurethane, polyester, polyamid or polyolefin, with a preference for polyurethane.
Such a string finally has a tensile strength of 3.0 to 5.5 cN/dtex.
In this case there is also only a reference to a geometric pattern of the island components, without stating any specific arrangement or advantages thereof, with the exception of rotational symmetry that, as indicated above, can also only be implemented or realised from the outside, and can therefore not be regarded as a specific characteristic of the island structure.
A known advantage with all these monofilament strings is that they still have a stiffness that is too high which allows for too little control over the ball, and that when playing hard or soft can be held responsible for a clearly different ball feeling, apart from the previously already mentioned classical disadvantages.